New approach to optimise soft focus effect

Wrinkles and fine lines in human skin are perceptible primarily as dark, nonreflective areas because of the way light falls and remains there. In contrast, if light is reflected and diffused, the wrinkle appears less visible.

The objective of an optical light diffuser is to prevent light from being trapped in the wrinkles while maintaining transparency. Obviously, the mechanical filling in of the lines with a thick material looks unnatural. Instead, cosmetic chemists have found ways to throw light into the wrinkles and immediately eliminate the dark that makes the crease so obvious. They use a material that generates an optical blurring but is still transparent enough to avoid the mask-like appearance – soft focus ingredients are required.

The objective of the study described is to demonstrate the soft focus effect of ingredients obtained by a novel patented technology through the evaluation of different optical parameters. Finally, two examples of applications are shown to illustrate the additional benefits of these specific ingredients: colour adapt foundation and “anti-wrinkle” make-up.

Theory of soft focus

From theoretical explanations, scientific publications1 detail the properties an ideal material should have to be an optimum light diffuser and to achieve the soft focus effect (Fig. 1).

Light absorption should be minimal. If the light is absorbed, then no light is reflected, which will result in a dark or greyish appearance.

Specular reflection (observed as gloss or lustre) should be minimal. Gloss or lustre makes the wrinkles more visible. Scattered reflection should be maximal. Light is reflected from all directions to provide an even light distribution.

Direct transmission should be minimal. Very transparent materials do not have enough optical effect.

Diffuse transmission should be maximal. Diffuse transmission can provide even light distribution.

Refractive index of the material should be close to that of the skin, about 1.5 – 1.6. The colour of the material is usually beige, skin-tone or white.

The particle shape should allow maximal scattered reflection and diffuse transmission. Optimal particle size should be 2 – 20 microns.

The ingredient(s) have to be acceptable for cosmetic use globally. In conclusion, an optimum soft focus ingredient could be defined as a matte, transparent and light diffuser material.

Materials and methods

A novel patented technology
The evolution of manufacturing techniques allows the creation of more and more sophisticated cosmetic ingredients. The technology described here is for a new generation of materials.

Hybridisation is a technology based on the optimised combination of two conventional cosmetic materials to create optimal properties which did not exist, completely or partially, in the raw materials used separately. More precisely, the purpose here is to optimise the optical diffusing properties of two raw materials by creating synergistic performances.

Two different processes have been developed to highlight the efficiency of this global technology in soft focus effect. Process number 1: Particles of a mineral oxide are incorporated inside a mineral matrix. For this, nanofine titanium dioxide was trapped inside amorphous alumina (Fig. 2). The resulting product is an amorphous complex of alumino-titanium oxide, Product A. Process number 2: Particles of another mineral oxide are associated outside a spherical organic matrix. For this, silica was incorporated at the surface of methylmethacrylate crosspolymer beads (Fig. 3). The resulting product is an hybrid spherical material.

This technology generates different products with different characteristics and different shapes. The objective of the experimental work is to show that the same advanced technology could lead to different products but with similar soft focus properties.

The experiments are based on the evaluation of three different parameters: mattifying properties, transparent material and light diffusing effect.

Determination of the mattifying properties of hybrid ingredient
Scientific considerations have demonstrated that gloss makes the wrinkles more visible. So, it is necessary to determine the ability of the hybrid ingredients to mattify a highly glossy substrate (nail polish lacquer) in order to contribute to an optimum light diffusion. For this experiment, each powder was dispersed at 5% in the nail polish lacquer and applied on a drawdown card. The gloss is measured by a glossmeter Micro- TRI-gloss from BYK Gardner at an angle of view of 60°.

The gloss values of hybrid powders are compared with those of the raw materials used for the hybridisation.
The glossier the film is, more the ingredients have mattifying properties.

Determination of the transparency and light diffusing properties
A specific experiment has been designed to determine the optical properties of the hybrid materials. The transparency and the light diffusing properties are evaluated through the same study of measurement of the Haze Index (H), in other words, the Soft Focus Index (H).

The Haze Index (H) gives a relation between the total diffuse transmission and total transmission (Fig. 4). The total transmission is defined as the addition of diffuse transmission and direct transmission.

The value of total transmission gives the transparency of a material. The more transparent is a substrate, the more the light is transmitted through this material. The Haze Index (H) gives an evaluation of the performance of optical blurring.

The more important is the H, the more efficiency is the light diffuser and higher is the soft focus effect. For this experiment, it is necessary to disperse 0.4 g of sample with 1.6 g of silicone by a Müller (50 rounds x 6 times), apply the sample to a glass plate to make film uniformly using applicator 0.025 mm and measure Haze Index (H) by Haze Meter HR-100.

Results and discussion

Mattifying properties of hybrid powders
Tables 1 and 2 provide the gloss values of the two hybrid products in comparison with their respective raw materials. The hybridisation technology improves the mattifying properties of ingredients.

Transparency evaluation
Tables 3 and 4 present the total transmission (%) of the hybrid powders in comparison with their respective ingredients. These results are directly obtained with the Haze meter. The values of total transmission are variable according to the nature of the materials. But, in a general way, the hybridisation technology does not modify deeply material transparency.

Light diffusing properties: the Haze Index (H)
Tables 5 and 6 give the values of total transmission and diffuse transmission measured by the Haze meter and the Haze Index (H) of the tested powders.

The transparency and the light diffusing properties are combined in Figure 4.

Hybridisation technology optimises the light diffusion for a higher balance between transparency and soft focus effect.

From theoretical studies, it is evident that the optimisation of the optical blurring effect could be completed by the adjustment of other physical parameters. Table 7 provides additional information supporting an higher soft focus result. Through two different shapes, two different natures of matrix, two different combinations of materials to obtain an optimised soft focus effect, the hybrid powders show an excellent balance between mattifying properties, transparency and light diffusing effect.

So, these experiments allow us to conclude that this hybridisation technology provides great optical performances for an optimised soft focus effect.

Applications

Colour adapting performance
The hybrid powder resulting from Process No.1 presents the additional benefit to be an innovative soft focus pigment adaptor. Thanks to advanced optical performances, this specific product has the ability to adapt the colour to the skin complexion (Fig. 5). Indeed, this material was introduced in a W/SI foundation (Table 8).

‘Anti-ageing’ make up
The product from the Process No.2 is completely different, both in nature and shape. Thus, the additional optical properties are very specific.

Table 9 presents the formulation of pore minimiser mattifying gel which illustrates perfectly the combination between make-up and skin care requirements (Figure 6).

Conclusion

The consumer sees a wrinkle and wants it to disappear. The soft focus materials provide an efficient solution for a more instantaneous “anti-ageing” visual effect. Through different experiments, the novel technology of hybridisation proves to be at the origin of the creation of ingredients with advanced optical properties and more precisely, with an optimised soft focus effect.

Acknowledgement
Thanks are due to all the technical teams which worked to make this innovative project successful.

Reference

1 Quantification of the Soft-Focus Effect. Dr. R. Emmert. Cosm. Toil., 111, 7, 1996.

ABSTRACT
Particles with soft focus effect are widely used to hide skin imperfections and wrinkles. It has been demonstrated that optimised soft focus effect is obtained when light characteristics are as follows:

A new technology, which is associating particles of alumina with particles of nanofine titanium dioxide, is presented. The refractive index and the transmittance and scattering properties are adjusted in order to optimise the s focus effect and achieve, in addition, colour adapting properties.

Comparative studies are carried out to evaluate the performance of this new range of ingredients against the traditional soft focus minerals such as alumina, talc or nanofine titanium dioxide. In particular, the study is showing the optimal Haze Index of this new ingredient, resulting from the combination of alumina and nanofine titanium dioxide.

A few cosmetic applications are described, such as “colour adapting” foundations and skin care products for the eye area.